The present invention relates to a pressure transmitter assembly, and more particularly, to a pressure transmitter assembly configuration for mounting a pressure sensor element of the pressure transmitter assembly to provide a more effective isolation of the pressure sensor element from outside sources of error, including temperature, stress . . . .
In current systems a silicon pressure sensor element is mounted onto a PYREX tube to provide stress isolation between the silicon pressure sensor element and a metal (or plastic) structure. This configuration accommodates mismatches in the thermal coefficient of expansion (TCE) between the materials. By mounting the pressure sensor element onto a PYREX tube (which is approximately a 1/2 inch long tube), stresses induced by the dissimilar materials are equalized before the stress effects the silicon pressure sensor element (sometimes referred to herein as a silicon die). This arrangement minimizes any errors in measuring the pressure due to the effects of changes in temperature on the mounting joint. The resulting configuration of these present systems result in a long cylindrical column relative to the silicon die, resulting in a structure that is subject to vibration and shock damage (due to the length to diameter ratios).
Thus there is provided by the present invention a mounting arrangement for the pressure sensor element which provides isolation from the vibration and stress without requiring a long bulky assembly. The present invention provides a low profile structure by turning the mounting structure such that it is essentially in the same plane as the surface of the silicon die, thereby resulting in the very low profile. Essentially all of the components are constrained into one plane, and allows for thermal isolation, and stress isolation to take place between the pressure port and the pressure sensor element. The pressure sensor element of the present invention is mounted on a ceramic structure having interlayer passages which form the pressure port and is coupled to the bottom side of the chip (i.e., silicon die). The ceramic mounting material provides the same function served by the PYREX tube in the previous systems; however, keeping the ceramic in the same plane as the silicon die surface reduces the vibration and shock damage tendency while still allowing flexure between the metal header and the sensor element. The resulting design of the present invention includes the pressure sensor element constrained in the same plane as the circuit leaving a flat structure which is much easier to handle both electrically and mechanically. In the present invention the ceramic mounting surface of the silicon die does not need to be TCE matched as closely to the silicon as in the previous configuration. Thus, many more common ceramics (and low cost ceramics) can be utilized because of the flexibility inherent in the structure which provides the stress isolation.